1. Field of the Invention
The present invention relates to a substrate processing apparatus including a focus ring.
2. Description of the Related Art
Recently, semiconductor wafers (hereinafter, simply referred to as ‘wafers’) from which semiconductor devices are fabricated have been enlarged, and accordingly, it is required that semiconductor devices be obtained from peripheral portions of wafers, for example, a range within 10 mm toward centers of wafers from peripheries of the wafers. However, since distribution of radicals in plasma used to process a wafer is affected by a temperature distribution of an object, a temperature of a peripheral portion of a wafer needs to be controlled to be nearly similar to temperatures of other portions on the wafer in order to perform a uniform process using radicals on the entire wafer. Therefore, conventionally, a technology for adjusting and cooling a temperature of a focus ring has been developed in order to reduce radiation heat of a focus ring.
However, when a temperature of an entire wafer is excessively lowered by cooling a focus ring, a resist film applied on the wafer as a pattern mask may be easily trimmed by plasma. Thus, in order to prevent a temperature of an entire wafer from excessively being lowered, a technology of providing an additional focus ring (hereinafter, referred to as an ‘outer focus ring’) on an outer side of the focus ring (hereinafter, referred to as an ‘inner focus ring’) that is cooled down, and then, instead of cooling the additional focus ring, actively heating the additional focus ring has been developed by the present applicant (for example, refer to Patent Document 1).
However, in general, in a gap between two components having temperatures largely different from each other, deposits are likely to be attached on the component having the lower temperature, and thus the present inventor identified that deposits are easily attached to the inner focus ring in a gap between the two focus rings, when the above so-called 2-partition focus ring including the inner focus ring and the outer focus ring is used.
Since the gap between the inner focus ring and the outer focus ring is narrow and it is difficult for plasma to enter the gap, it is difficult to remove deposits attached onto the inner focus ring by using an ashing process or the like. Therefore, in order to remove deposits, a chamber is opened to atmosphere to take out the inner focus ring, and deposits need to be cleaned from the inner focus ring. Accordingly, a working ratio of a substrate processing apparatus is degraded.
In addition, in the substrate processing apparatus, a susceptor on which the inner focus ring or the outer focus ring is placed is cooled down to a temperature that is lower than that of the inner focus ring, and thus a temperature difference between the inner focus ring and the susceptor is increased and deposits are also attached to the susceptor in a gap between the inner focus ring and the susceptor.
Since the gap between the inner focus ring and the susceptor is also narrow, the chamber is opened to atmosphere to take out the inner focus ring and expose the susceptor, and then the inner focus ring and the susceptor are cleaned in order to remove deposits. Accordingly, the working ratio of the substrate processing apparatus is also degraded.    (Patent Document 1) Japanese Patent Application No. 2010-021079